Triplet state spectroscopy and photofragment dynamics of N2+2

The photofragment spectrum of N2+2→N+(3Pg)+N+(3Pg) has been studied using a coaxial laser–ion beam spectrometer. Transitions from the excited 3Σ+u(v=0,1) state of N2+2 to the predissociative 3Πg(v=0) state result in two bands with dense rotational structure at 15 300 and 13 100 cm−1. A complete analysis of the 27 rotational branches associated with the 3Πg(v=0)←3Σ+u(v=0) transition provides bond lengths and spectroscopic constants for both states. A perturbation is observed in the (0,0) band, caused by the interaction of 3Σ+u(v=0) with 3Πu(v≊10). From a deperturbation analysis, the coupling constants and the energy difference between the 3Πu(v≊10) and 3Σ+u(v=0) states are determined—ξ=1.5±0.1 cm−1, η=0.220±0.003 cm−1, and Tpert=365±25 cm−1. A broad unstructured band at 16 400 cm−1 arises from a transition out of v=0 in the 3Σ+u state into a very short-lived v=1 level of the 3Πg state. Vibrational spacings between v=0 and v=1 in both electronic states are determined—3Σ+uω0=2210±20 cm−1 and 3Πg ω0≊1100 cm−1. The fragmentation of N2+2 is explored by measuring the dependence of predissociation lifetimes on the rotational quantum number of the 3Πg(v=0) state. Experimentally determined lifetimes of 50–70 ps for N′=2–17 are almost independent of N′ and indicate that the predissociation occurs by the interaction of 3Πg(v=0) with the 3Σ−g continuum rather than by tunneling through the 3Πg barrier.